The Nuclear Regulatory Commission says in a statement Tuesday that the leak was contained to the building. The leak forced operators of the plant in Van Buren County's Covert Township to remove it from service Sunday. Repairs are planned. The NRC says it has no immediate safety concerns.

The NRC says the leak contained "very low levels of tritium" and will be treated as radioactive liquid waste.

The plant says the leak couldn't be isolated or repaired with the plant in service.

The plant has been designated by the NRC as one of the nation's four worst-performing nuclear plants.